Puppies that are over-tired will often begin to play-bite without thinking, and their bites can get hard and careless.

Tired puppies can also get very irritable and snappy, just like over-tired children. Giving them time out to sleep, with frequent rest periods throughout the day, will usually result in softer mouthing and a more thoughtful approach.

Puppies frequently get over-tired if there are children in the household who may be keeping a very young puppy actively awake and engaged well past the time when it would normally have been resting and sleeping. Putting the puppy into a quiet room for periods of time out when it is tired, and before it gets over-tired, will make it less likely to become careless with its teeth when playing.